Organic acid fluorides are used as starting materials for a variety of fluorine-containing organic compounds, especially for the perfluorovinyl ethers that are important as comonomers constituting polymers such as resins and elastomers. For example, an oligomerization reaction with hexafluoropropylene oxide (HFPO) as represented by the formula below can be considered as an important reaction.RCOF+n(HFPO)→RCF2O(CF(CF3)CF2O)n-1CF(CF3)COF
The product of this reaction is also important as a precursor of the aforementioned perfluorovinyl ethers, and as a starting material for producing fluorine-containing ethers, fluorine-containing alcohols, etc. It is known to conduct this reaction in an aprotic polar organic solvent in the presence of a catalyst such as alkali metal halides, alkyl ureas, quaternary ammonium halides or the like. However, when the starting material contains even small amounts of hydrogen fluoride, hydrogen chloride or like acidic gases, water, carboxylic acid, or the like, a phenomenon occurs in which expensive catalysts are deactivated. The presence of water causes an RCOF— type compound to decompose into RCOOH and HF. Therefore, insufficient drying through carelessness may well generate HF, so that the catalyst may be easily inactivated. For instance, COF2 is generated as a by-product in producing hexafluoropropylene oxide by oxidizing hexafluoropropylene with oxygen, and HF is present along with this COF2. Therefore, such COF2, when used as a starting material in the aforementioned oligomerization reaction, poses a problem of enzymatic deactivation due to the presence of HF. Given the above circumstance, a demand has existed for the development of a process for removing the acids present in RCOF in order to prevent catalyst deactivation.
Among organic acid fluorides, COF2 is a hopeful candidate for an etching or chamber cleaning gas for use in semiconductor production free from the concern of any contribution to global warming. However, as described above, acids are usually present when COF2 is produced, thereby posing problems such as corroding equipment and transportation containers due to the presence of the acids. For this reason, the development of a process for acid removal is also strongly desired.
Because, as mentioned above, RCOF is unstable with respect to water, deacidifying agents such as Al2O3, SiO2 and like that produce water by reaction with HF cannot be used, not to mention conventional aqueous alkaline solutions. Furthermore, deacidifying agents containing ammonia or primary or secondary amines form amides with RCOF and thereby bind starting materials, making the use of such deacidifying agents impossible in the aforementioned oligomerization reaction.
In contrast, sodium fluoride, potassium fluoride and the like are known deacidifying agents that do not generate water even after adsorbing HF. However, they have disadvantages, such as poor deacidifying efficiency requiring large-scale treatment devices to remove HF to the degree that the deacidified RCOF can withstand the oligomerization reaction, and significant energy consumption requiring high temperatures of 350° C. or more to recycle these deacidifying agents by thermally desorbing the adsorbed acids.
Rectification is an example of a process that does not require the use of a deacidifying agent. However, despite the fact that COF2 and HF, for example, have a boiling point difference of over 100° C., it is not easy to separate COF2 and HF through conventional rectification processes, making the conventional processes inappropriate and requiring a complex process.
As described above, there is currently no useful process for removing acids present alongside RCOF to prevent catalyst deactivation or the corrosion of equipment and transportation containers when RCOF is used as a gas employed in semiconductor production.